The art of cleaning generally consists of multiple zones of treatment; namely, a wash zone, a rinse zone and a dry zone. The wash zone typically contain a prewash section, a wash section and an air isolation section. In addition, there is a rinse section which typically includes a first rinse section to wash away the chemical from the wash section, a rinse section, a final rinse section and an isolation section. The final drying section generally contains an air isolation section, and the heated air dry section. A central exhaust system located at the top of the entire apparatus acts to extract fumes generated from the washing actions, which are extracted by the central exhaust blower external to the cleaning apparatus. There is also a conveyor transport system which runs across the entire length of the various zones of treatment. This conveyor carries the device to be cleaned and moves the devices through the various treatment zones for cleaning and drying.
Cleaning equipment in the art generally include commercial spray nozzles attached to a spray manifold or hose, and held across the path of the device to be washed and cleaned. These nozzles are usually very large and bulky in diameter and provides various types of spray cones and angles of discharge (see angle .alpha. as shown in FIG. 3). When these nozzles are attached a cross the spray manifold or hose, they cannot achieve close pitching when attached in a straight line. Thus a spray angle coverage is the only means by which these spray nozzles reach the entire surface of the devices to be cleaned. This spray angulation causes the edges of the devices to experience a decrease in fluid energy as in the decrease of mass momentum of fluid motion. Advancement in miniaturization of semi-conductor chips with the creation of micro-ball grid area packages and chip scale packages has seen the input-output interconnect leads being replaced by solder balls, with a pitch of around 1.0 to 1.5 mm. With the bulky size of the spray nozzles, cleaning of such closely packed devices become ineffective.
Conventional spray manifold and hoses have angled spray jets which have a direction of spray perpendicular to the conveyor belt (see angle .theta. in FIG. 17) i.e. direction of spray of 0.degree. . With respect to the vertical axis as shown in line 888 in FIG. 17A. These types of design limits the cleaning parameters which are much needed to enhance cleaning actions. When angled spray jets with a 0.degree. direction of spray are used to clean parts having very light weight, such as a plastic ball grid array (BGA) strip, the mesh-type conveyor belt which is suppose to transport the strip across the various zones may not function effectively. The sandwich effect of a strong top and bottom spray at high velocity and pressure may pin the device at a stationary position due to slippage relative to the belt. This problem is compounded by the fact that most semi-conductor packages are cleaned in the"dead-bug" position, with the plastic packaging in contact with the conveyor mesh. Due to the low coefficient of friction between the plastic and the mesh-type conveyor belt, slippage is aggravated. When the package slips and travels inconsistently, the travel time and spray contact time (i.e. cleaning time) becomes inaccurate. This results in loss of yield and cleaning efficiency of the conventional equipment.
Conventional spray manifold and hoses also use a fixed tunnel width and height design with specially customized nozzles. Physical principles dictate that a severe pressure drop would result across these conduit, resulting in a significant drop in velocity of the sprays which are directly proportional to the distance from the fluid source.
Conventional in-line cleaning equipment are also known to provide notched conveyors, which provide lane guiding to prevent lateral movement of the devices along the conveyor belt. The notches, however, are limiting when the type of devices to be cleaned is changed during batch production because of the amount of time needed to completely change to a different. type of belt with different notch spacing to accommodate the varying package sizes. Dedicated notch conveyor is also termed bottom guiding conveyor for multi-lane strips cleaning, and is also very difficult to convert when the size, of the semi-conductor package change during actual production.
The conveyor systems in cleaning apparatus as known in the art are also designed with one belt spanning the various zones of cleaning. Fluid tends to remain on the conveyor mesh after cleaning, and takes time to dislodge by gravity. The time to dislodge the adhering fluid is often longer than the time it takes for a device to move across zones. Thus the prior art design permits carry-over of fluids from one cleaning zone to the next, resulting in cross-contamination.
The conveyor belts in the art are commonly of a cross mesh-type which gives the advantage of ease of tension without gears. However, the cross meshes have the disadvantage of creating shadows on the devices to be cleaned. This means that some portions of the devices are inaccessible for cleaning due to the physical presence of the cross mesh.
Present in-line cleaners are also prone to variable cleaning effectiveness due to load variation. When the load increases due to production throughput, and enters the cleaning apparatus in a staggered or random manner in their respective lanes, the dynamic load will reduce the conveyor speed. The speed of such conveyors is inversely proportional to the total weight of the load. This results in uneven cleaning time and subjects the devices to non-uniform parameters of cleaning, affecting the yield of the cleaning equipment.
Prior art cleaning technology in general make little effort to control fluid consumption and prevent loss of cleaning fluid. Typically, the wash fluid is allowed to find its own path towards a drip tray collecting device. However, due to the carry-over effect mentioned previously, and a lack of features designed for conservation, fluid recovery is left to chance, and wash fluid is often allowed to dissipate into the exhaust system or into the next zone. Poor recovery of fluid results in high operating costs.